Ashida H, Tamaki H, Fujimoto T, Yamamoto K, Kumagai H
Division of Integrated Life Science, Graduate School of Biostudies, Kyoto University, Japan.
Arch Biochem Biophys. 2000 Dec 15;384(2):305-10. doi: 10.1006/abbi.2000.2114.
Alpha-N-acetylgalactosaminidase (alpha-GalNAc-ase; EC 3.2.1.49) is an exoglycosidase specific for the hydrolysis of terminal alpha-linked N-acetylgalactosamine in various sugar chains. The cDNA, nagA, encoding alpha-GalNAc-ase from Acremonium sp. was cloned, sequenced, and expressed in yeast Saccharomyces cerevisiae. The nagA contains an open reading frame which encodes for 547 amino acid residues including 21 residues of a signal peptide in its N-terminal. The calculated molecular mass of mature protein from the deduced amino acid sequence of nagA is 57260 Da, which corresponds to the value obtained from SDS-PAGE of native and recombinant enzymes treated with endo-beta-N-acetylglucosaminidase H. The amino acid sequence of NagA showed significant similarity to those of eukaryotic alpha-GalNAc-ases and alpha-galactosidases (alpha-Gal-ases), particularly alpha-Gal-ase A (AglA) from Aspergillus niger. Phylogenetic analysis revealed that NagA does not belong to the cluster of vertebrate alpha-GalNAc-ase and alpha-Gal-ase but forms another cluster with AglA and yeast alpha-Gal-ases. Thus, the evolutionary origin of the fungal alpha-GalNAc-ase is suggested to be different from that of vertebrate alpha-GalNAc-ase. This is the first report of a microbial alpha-GalNAc-ase gene.
α-N-乙酰半乳糖胺酶（α-GalNAc酶；EC 3.2.1.49）是一种外切糖苷酶，特异性水解各种糖链中末端α-连接的N-乙酰半乳糖胺。从顶孢霉属克隆、测序并在酿酒酵母中表达了编码α-GalNAc酶的cDNA，即nagA。nagA包含一个开放阅读框，编码547个氨基酸残基，其N端包括21个信号肽残基。根据nagA推导的氨基酸序列计算出的成熟蛋白分子量为57260 Da，这与用内切β-N-乙酰葡糖胺酶H处理的天然和重组酶的SDS-PAGE结果一致。NagA的氨基酸序列与真核α-GalNAc酶和α-半乳糖苷酶（α-Gal酶）的序列有显著相似性，特别是与黑曲霉的α-Gal酶A（AglA）。系统发育分析表明，NagA不属于脊椎动物α-GalNAc酶和α-Gal酶的聚类，而是与AglA和酵母α-Gal酶形成另一个聚类。因此，真菌α-GalNAc酶的进化起源被认为与脊椎动物α-GalNAc酶不同。这是关于微生物α-GalNAc酶基因的首次报道。
